Polycrystalline ultra-hard constructions, such as polycrystalline diamond (PCD) materials and PCD elements formed therefrom, are well known in the art. Conventional PCD is formed by subjecting diamond grains to processing conditions of extremely high pressure and high temperature in the presence of a suitable solvent catalyst material, wherein the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The solvent catalyst material can be combined with the diamond grains prior to processing or the solvent catalyst material can be provided from an outside source, e.g., from an adjacent substrate body or the like that contains the solvent catalyst material, by infiltration during processing. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used for forming conventional PCD include metals selected from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is disposed within interstitial regions of the PCD microstructure that exist between the bonded together diamond grains or crystals.
A problem known to exist with such conventional PCD materials is thermal degradation due to differential thermal expansion characteristics between the interstitial solvent catalyst material and the bonded together diamond crystals. Such differential thermal expansion is known to occur at temperatures starting at about 400° C., causing ruptures to occur in the diamond-to-diamond bonding, and resulting in the formation of cracks and chips in the PCD structure.
Another problem known to exist with conventional PCD materials also relates to the presence of the solvent catalyst material in the interstitial regions of the microstructure and the adherence of the solvent catalyst to the diamond crystals that is known to cause another form of thermal degradation. Specifically, the solvent catalyst material is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of such PCD materials to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in PCD are known in the art. Generally, these attempts have involved treating the PCD to remove the solvent catalyst material therefrom. PCD materials that have been treated in this manner are referred to as being thermally stable. Such thermally stable polycrystalline diamond (TSP) materials have a material microstructure comprising a polycrystalline matrix phase of bonded together diamond crystals, and a remaining phase comprising a plurality of pores or voids interposed between the diamond crystals resulting from the removal of the solvent catalyst material.
Such TSP material formed from PCD typically does not include a metallic substrate attached thereto, as any metal substrate is either removed from the PCD before treatment, or if not removed beforehand, falls away from the PCD body after treatment by the removal of the solvent metal catalyst at the interface previously joining the PCD body to the substrate.
A problem known to exist with using such TSP materials in conjunction with known cutting and/or wear devices such as subterranean drill bits or the like is the need to attach the TSP material to a substrate to provide an overall construction that permits attachment with a desired cutting or wear device by conventional technique, such as by welding, brazing or the like. However, such TSP materials typically have a poor wetablity and have a coefficient of thermal expansion that is significantly different from that of substrate materials conventionally used for attaching polycrystalline bodies thereto, thereby making it very difficult to bond the TSP material to such conventionally used substrates.
Attempts have been made to form compact constructions from TSP material by brazing the TSP body to a desired substrate. However, such compact constructions comprising the TSP material brazed together with a substrate, e.g., formed from cemented tungsten carbide, are known to be easily fractured along the braze joint, which fracture is believed to be caused by the formation of voids and residual thermal stresses in the braze joint during the process of brazing. Thus, compacts formed by brazing such TSP material to such conventional types of substrates are known to be vulnerable to fatigue and/or impact damage at the interface when placed into a wear and/or cutting operation. Accordingly, conventional TSP compacts formed in this manner typically have a reduced service life that is not desired in most cutting and/or wear applications.
An alternative approach for using conventional TSP materials in wear and/or cutting application has been to avoid the use of a substrate completely, and rather attach the TSP material or body directly to the intended cutting and/or wear device, i.e., without the use of an intervening substrate. However, because such TSP materials lack either a metallic material or a metallic substrate, they cannot (e.g., when configured as a cutting element for use in a subterranean drill bit) be attached to a drill bit by conventional brazing process. Thus, use of such TSP materials in this particular application necessitates that the TSP material or body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
It is, therefore, desired that polycrystalline ultra-hard constructions be provided in the form of a compact including a polycrystalline ultra-hard material having a desired degree of thermal stability, and that is attached to a substrate. It is desired that such construction have properties of improved bond strength when compared to the above-noted conventional TSP constructions. It is also desired that such polycrystalline ultra-hard constructions be provided in a manner that display reduced residual thermal stress when compared to conventional TSP compact constructions. It is further desired that polycrystalline ultra-hard constructions be provided comprising a support structure that is specially designed to enhance the strength of the construction and/or that provides reduced residual thermal stress, and/or that provides an improved attachment with the cutting and/or wear device, when compared to conventional TSP compact constructions lacking such support structure.